1. Field of the Invention
The present invention relates to a turbomolecular pump including a plurality of alternatively axially arranged one behind another, rotor and stator discs provided with blades, with the blades located in vicinity of the high-vacuum side having a blade angle that is steeper than a blade angle of the blades located in the vicinity of the vacuum side. The present invention also relates to a method of manufacturing of rotor and stator discs provided with blades having such blade angles for the turbomolecular pump.
2. Description of the Prior Art
Turbomolecular pumps of the type described above are well known. E.g., such turbomolecular pumps are disclosed in German Publications DE 2 035 063 B3 and DE 27 17 366 B2. The blades of these pumps have a cross-section of a parallelogram. The blade angle amounts to, dependent on an axial position of the blade, from 25° to 40°.
German Publication DE 101 03 230 A1 discloses a turbomolecular pump in which the cross-section of a blade substantially deviates from a parallelogram and has a shape of a wing. The medium blade angle amounts to about 45°.
German Publication DE 72 37 362 U1 discloses a turbomolecular pump in which the blades of a first group of blades, which are arranged at a suction side, the so-called suction group A, have a blade angle from 30° to 40°, and the blades of a second group, so-called compression group B, include the blades of the remaining stages and having a blade angle from 17° to 30°. The second group, the compression group B, can be divided in two sub-groups the blades of which have a blade angle, respectively, from 25° to 30° and from 17° to 25°.
The turbomolecular pump of the model Alcatel ATH 1600M has flat blades with a blade angle greater than 19°.
Pump-active components of a turbomolecular pump are formed by rotor and stator discs which are provided with blades and which are alternatively axially arranged one behind the other. The pumping effect is obtained in a known manner by cooperation of the rotor and stator discs.
The main characteristics of a turbomolecular pump are compression ratio and suction speed. The characteristics are primarily determined by the following parameters: circumferential speed of the blade ring of the rotor discs, number of blades, blade angle of the blades, and stage distribution of different discs of the entire disc set. Within the stages, the blade angle of a blade diminishes from the suction opening to the outlet opening.
Heat is generated primarily in the compression or outlet stages. This heat can lead to an undesired heating of the rotor. Besides, at high fore-vacuum pressures, these stages are very important for the fore-vacuum compatibility and the consumption power. The conventional turbomolecular pumps are generally characterized by unsatisfactory fore-vacuum compatibility, high consumption power, and strong heating of the rotor.
Accordingly, an object of the present invention is to provide a turbomolecular pump in which a significant heat generation and consumption power are prevented and a good fore-vacuum compatibility and compression are obtained.